I got this off the babycentre website. Hope it helps...
How can I prevent these cramps?
Try these tips for keeping leg cramps at bay:
• Avoid standing or sitting with your legs crossed for long periods of time.
• Stretch your calf muscles regularly during the day and several times before you go to bed.
• Rotate your ankles and wiggle your toes when you sit, eat dinner, or watch TV.
• Take a walk every day, unless your midwife or doctor has advised you not to exercise.
• Avoid getting too tired. Lie down on your left side to improve circulation to and from your legs.
• Stay hydrated during the day by drinking water regularly.
• Try a warm bath before bed to relax your muscles.
• There's some evidence that taking a magnesium supplement in addition to a prenatal vitamin may help some women. Check with your provider before taking any kind of supplement during pregnancy.
You may have heard that having leg cramps is a sign that you need more calcium, and that calcium supplements will relieve the problem. Though it's certainly important to get enough calcium, there's no good evidence that taking extra calcium will help prevent leg cramps during pregnancy. In fact, in one well-designed study, pregnant women taking calcium got no more relief from leg cramps than those taking a placebo.
What's the best way to relieve a cramp when I get one?
If you do get a cramp, immediately stretch your calf muscles: Straighten your leg, heel first, and gently flex your toes back toward your shins. It might hurt at first, but it will ease the spasm and the pain will gradually go away.
You can try to relax the cramp by massaging the muscle or warming it with a hot water bottle. Walking around for a few minutes may help too.